Ultrasonic cutters are currently used to cut sheet and other materials using a knife powered by an ultrasonic transducer. One application of ultrasonic cutters may be found in the field of composite materials where multiple layers or plies of uncured composite material forming a lay-up may be simultaneously cut to a desired shape using an ultrasonically powered knife. In some cases, the ultrasonic cutter may be mounted on a CNC (computer numerical control) controlled machine tool that includes an automatic tape laying head capable of laying down and cutting multiple, overlapping layers of composite tape.
The process of cutting the composite material is relatively slow in comparison to the rate at which the tape may be applied. The speed of the cutting process may be determined, in part, by the maximum feed rate of the knife through the material and depth of cut. Thicker parts require multiple passes in order to fully cut through all plies of material, with each pass of the cutter being deeper than the last. Currently, an open-loop ply cutting process is used that requires constant operator monitoring and manual adjustment of the feed rate override dial, which may result in suboptimal cutting operations, including suboptimal cutting speed. Knife feed rates are manually adjusted by an operator during cutting based on observed fluctuations in the ultrasonic power meter. Perceived “safe” power levels are maintained by overriding the programmed feed rate, which may result in cutting times that are less than optimal. Moreover, operators may not be able to detect transient or peak load conditions and react quickly enough to decrease feed rates before possible knife malfunction occurs. In some cases, excessive feed rates may also result in suboptimal cutter operation.
The prior art includes an adaptive control apparatus having a load detector that detects a load which acts on a cutting tool during a machining operation of a workpiece. Such adaptive control techniques have not, however, been applied to CNC ultrasonic cutters used to cut multiple plies of composite material.
Accordingly, there is a need for a method and system for cutting plies of composite material using a CNC controlled ultrasonic cutter that employs adaptive control in order to optimize feed rate and/or reduce knife damage and cutting errors.